The human fusional mechanism is responsible for the unification of two disparate retinal images in the interest of single binocular vision. Fusional response to retinal image disparity is made up of two components: 1) A central component whose magnitude is limited to the extent of Panum's fusional areas and 2) A motor component in the form of compensatory eye movements. Very little is known about the way in which fusional information (disparity between the two retinal images) is assessed at the retinas and is acted upon at higher centers. My long range objective is to investigate how fusional response is mediated. To this end it is proposed to 1) Explore the way in which disparity information is assessed within Panum's fusional areas. 2) Investigate how fusional response is apportioned between its central and motor components. 3) Examine the operating characteristics of the central mechanism that processes or acts upon fusional information in the interest of binocular vision. 4) Investigate the characteristics of the motor components: mode of operation, control, and temporal characteristics. The results of these experiments will provide basic information that is essential to the understanding of human fusional response underlying binocular vision.